MC68HC912BL16 Datasheet, PDF (90/128 Pages) Freescale Semiconductor, Inc – 16-Bit Microcontroller

Freescale Semiconductor, Inc.
BTST — Baud Register Test
Reserved for test function
BSPL — Baud Rate Counter Split
Reserved for test function
BRLD — Baud Rate Reload
Reserved for test function
SC0CR1 — SCI Control Register 1
Bit 7
6
5
4
3
2
LOOPS WOMS RSRC
M
WAKE
ILT
RESET:
0
0
0
0
0
0
$00C2
1
Bit 0
PE
PT
0
0
Read or write anytime.
LOOPS — SCI LOOP Mode/Single Wire Mode Enable
0 = SCI transmit and receive sections operate normally.
1 = SCI receive section is disconnected from the RXD pin and the RXD pin is available as general
purpose I/O. The receiver input is determined by the RSRC bit. The transmitter output is con-
trolled by the associated DDRS bit. Both the transmitter and the receiver must be enabled to
use the LOOP or the single wire mode.
If the DDRS bit associated with the TXD pin is set during the LOOPS = 1, the TXD pin outputs the SCI
waveform. If the DDRS bit associated with the TXD pin is clear during the LOOPS = 1, the TXD pin be-
comes high (IDLE line state) for RSRC = 0 and high impedance for RSRC = 1. Refer to Table 30.
WOMS — Wired-Or Mode for Serial Pins
This bit controls the two pins (TXD and RXD) associated with the SCI section.
0 = Pins operate in a normal mode with both high and low drive capability. To affect the RXD bit,
that bit would have to be configured as an output (via DDRS) which is the single wire case when
using the SCI. WOMS bit still affects general-purpose output on TXD and RXD pins when SCI
is not using these pins.
1 = Each pin operates in an open drain fashion if that pin is declared as an output.
RSRC — Receiver Source
When LOOPS = 1, the RSRC bit determines the internal feedback path for the receiver.
0 = Receiver input is connected to the transmitter internally (not TXD pin)
1 = Receiver input is connected to the TXD pin
Table 30 Loop Mode Functions
LOOPS RSRC
0
x
1
0
1
0
1
0
1
1
1
1
1
1
DDS1
x
0
1
1
0
1
1
WOMS
Function of Port S Bit 1
x Normal Operations
0/1 LOOP mode without TXD output (TXD = High Impedance)
0 LOOP mode with TXD output (CMOS)
1 LOOP mode with TXD output (open-drain)
x
Single wire mode without TXD output
(the pin is used as receiver input only, TXD = High Impedance)
0
Single wire mode with TXD output
(the output is also fed back to receiver input, CMOS)
1 Single wire mode for the receiving and transmitting (open-drain)
M — Mode (select character format)
0 = One start, eight data, one stop bit
1 = One start, eight data, ninth data, one stop bit
MC68HC912BL16
90
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